Location Services (LCS) is becoming more and more used by operators and governments today.
Assisted Global Positioning System (AGPS) provides the highest accuracy of all methods available for positioning of a portable communication device such as a Mobile Station (MS) or User Equipment (UE) today. AGPS uses mobile network data combined with satellite data to assist the trilateration of satellites enabling the determination of a position fix. The accuracy of an AGPS position is typically within 10-15 m of ground truth.
There are however situations where insufficient knowledge of the mobile network cell structure makes AGPS less accurate or fail completely. This is especially true for disaster areas where infrastructure has been damaged and temporary mobile base stations must be taken into use.
This disclosure is an attempt to enhance the success rate of AGPS usage in such situations.
Compared to stand-alone handheld Global Positioning System (GPS) devices, a mobile phone carries a smaller GPS antenna and has much less battery capacity to use for GPS measurements. In order to use the integrated GPS chip only during a positioning attempt, i.e. only during limited times, the chip needs to acquire satellite signals very fast. The mobile phone cannot afford to scan the whole sky to obtain signals from relevant satellites since it would take too long a time and the power consumption of repeated scans would deplete the relatively small battery. The mobile needs help to only scan a smaller part of the sky where signals from satellites detectable from its current location can be acquired.
Therefore, AGPS positioning needs a reference location of where the UE is in order to obtain a search window in the sky where to find satellites detectable given the reference location. The reference location may however be a rough estimate of where the UE is. The reference location can be crucial to the algorithms that calculate the AGPS position, since the calculations are in part done by an iterative Taylor search that needs a starting point. The closer the starting point is to the actual true position, the faster the position fix can be determined. In AGPS terms, the required time to determine a position fix is called Time To First Fix (TTFF). The determination of a proper reference location is therefore one of the key elements in obtaining an AGPS position. It must not be too inaccurate or the AGPS measurements will fail and no position fix can be determined.
The reference location normally used today in AGPS solutions is the location of the Base Transceiver Station (BTS) serving the UE at the time of the positioning attempt. Using its location, the UE knows where to start its measurements and where to acquire satellites. This gives much less battery consumption, and enables higher sensitivity of the chipset for more accurate measurements.
The location of the serving BTS or Node B is typically taken from the cell data distributed by the Operations Support System (OSS) and used by a positioning system for a range of purposes, one being the distribution or usage of reference locations during AGPS positioning.
The OSS is feeding the positioning system with network data continuously. However, keeping the network data updated is not an easy task for today's large networks, which may be in scales of hundreds of thousands cells or more. Since the OSS load cycle can take several days to complete, a change in the cell network structure might not be reflected at once. Without updated network data, an accurate reference location cannot be obtained for AGPS, causing the positioning to fail. The result is loss of AGPS capability in the unknown cell areas and reduced yield of the AGPS service in general.
Many chipsets used in UEs today require a reference location accurate within less than 100 km, or they will face severe problems, i.e. typically fail completely. Therefore the reference location must be chosen wisely. Without useful network data this becomes increasingly difficult.
Feeding of updated network data by the OSS may be a problem in disaster areas and in areas hit by an earthquake, to mention two examples.
In disaster areas this is clearly a problem, since there are often damages to the network infrastructure at the same time as the need of location information for emergency services increases. Search and rescue missions, evacuations, and/or supply deliveries would all benefit from knowing where the people in need are located. Emergency call (911, 112, etc) volumes tend to be high near disaster sites and pinpointing a caller's location can be a matter of life and death.
The risk of an earthquake hitting rural and suburban areas somewhere in the U.S.A. at 8:00 PM, may be higher than we wish. This could in addition result in infrastructural damages involving damages to several BTSs or Node Bs in the network covering the area, causing positioning problems. An operator serving the hit areas would put up mobile temporary base stations with a few hours delay to maintain coverage for emergency calls and normal voice traffic. These temporary sites may however not be reflected in the OSS cell data, since the OSS load cycle can take several days to complete. In addition, they may also be dismantled and moved again before the OSS eventually feeds the positioning system. The BTSs or Node Bs may be highly mobile, for instance mounted on trucks, and are typically placed where needed most at the moment.
People calling 911, 112 or the like from phones served by one of these temporary—and for the OSS and positioning system yet unknown—cells cannot be positioned with any level of accuracy typically produced by positioning systems of today. Positioning with Cell Global Identity (CGI) or Service Area Identifier (SAI) accuracy, that is positioning based on the serving cell location, is made impossible since the location of the mobile BTS or Node B is still unknown to the network. AGPS positioning might fail due to the absence of an accurate reference location, possibly caused by missing cell information.
In the two examples described above, it would not be possible to achieve accurate positioning due to the use of cells, which location is unknown to the position system. These positioning problems may thus occur in areas where emergency positioning may be of outmost importance and AGPS accuracy could save lives.
Thus, there is a need for a novel positioning method enabling high accuracy positioning in cells unknown to the positioning system.
Hence, an improved positioning method would be most advantageous and could thus even save lives of human beings.